The main object of the present invention is to provide a low pressure fuel injecting device for the two-stroke gasline engine so as to replace the conventional carburetor and to overcome the drawbacks of the high exhaust pollution and the high fuel consumption rate of the conventional two-stroke gasoline engine.
The major problem of causing a high fuel consumption rate and high pollution is that during the scavenging process, a part of the fresh mixture newly sucked into the cylinder escapes out together with the exhaust, i.e., the so-called short-circuit of fuel; the part which escapes out is usually ranging from 25-40% of the fresh mixture. In order to solve the aforesaid problems, adopting an in-cylinder fuel injection to replace fuel-and-air premixing of conventional carburetors will be an effective method, and the throttle body is only utilized to control the intake air flow without metering fuel, so that during the scavenging process, only the pure air is sucked into the cylinder. After the scavenging process is ended, the injector will inject fuel into the cylinder for combustion. This in-cylinder injecting system can eliminate the drawback of the short-circuit of fuel; however, on the prior arts, there are technical difficulties that have to be overcome.
According to conventional injection technique for a two-stroke diesel engine, the injector is mounted on the cylinder head. After the scavenging process is ended, and the piston closes the exhaust port, the injector will inject the diesel fuel so as to prevent the short-circuit of fuel from occurring. However, in order to prevent the fuel inside the injector from being vaporized caused by the heat soak from the high temperature of the cylinder head, the pressure of the fuel has to be extremely elevated to be higher than the "Reid vapor pressure" of the fuel under the in-cylinder highest temperature. Such a system is called a high pressure injection, which needs high precision components such as injection, pump, nozzle, tubing . . . etc. Therefore, from the standpoint of cost, it has never been successfully commercialized to a two-stroke gasoline engine.
Though the current fuel injection system usually used in four-stroke gasoline engine; is a low pressure one, in which the fuel pressure ranges from 1 kg/cm.sup.2 to 3 kg/cm.sup.2, the fuel is injected into the intake manifold or the throttle valve, i.e., the so-called "outside of cylinder" injection method. The environment condition of the aforesaid injection position is simple. In case of such a low pressure injection method being used inside a cylinder, the nozzle of the injector is susceptible to being fould on its tip, and the fuel inside the nossle is also susceptible to being vaporized under the heat soak from the cylinder; the nozzle will be unable to maintain its metering accuracy any longer as a result of fouling on its tip and fuel vaporizing inside. The main factors of nozzle tip fouling are caused by the blowing of exhaust gas and the carbonization of residual fuel drop after injection, and under such a low pressure, it is difficult for the fuel flow to remove the carbon deposited. Specifically, no matter what a hole type or needle type of the current injector, is used, the cross sectional area of its nozzle outlet determines the flow rate of fuel injected; therefore, a nozzle deposited with carbon would affect the fuel flow rate desired.
Moreover, the electro-magnetic valve assembly in the injector could lose its normal dynamic characteristics as a result of long time wear-and-tear and material fatigue (such as spring parts). Almost all the conventional gasoline injectors are of fixed structure type, and whenever their dynamic characteristics are out of order, they will be unable to repair and correct.